Blood pressure measurement techniques are generally put in two broad classes: instant and continuous. Instant techniques of blood pressure measurement, involve some kind of sensor working for a short period of time, such as cuff (non-invasive) or catheter (invasive) out of which an instant blood pressure data is derived. The continuous techniques allow of measurement of blood pressure values continuously for a defined period of time, with improved patient comfort and safety, but usually at the expense of accuracy.
Photoplethysmography or photoplethysmographic (PPG) systems have been used in an attempt to measure various blood flow characteristics including, but not limited to, the blood-oxygen saturation of hemoglobin in arterial blood, the volume of individual blood pulsations supplying the tissue, and the rate of blood pulsations corresponding to each heartbeat of a patient. Attempts at measuring some of these characteristics have used of a non-invasive sensor which scatters light through a portion of the patient's tissue where blood is perfused through the tissue, and optically senses the absorption of light in such tissue. This is a good candidate for the continuous blood pressure monitoring.
Typically PPG measurement systems include an optical sensor for an attachment to the tip of patient's appendage (e.g., a finger, earlobe and others). The sensor directs light signals into the appendage where the sensor is attached. Some portion of light is absorbed and a remaining portion passes through patient tissue. The intensity of the light passing through the tissue is monitored by the optical sensor. The intensity related signals produced by the sensor are used to compute blood parameters based on blood flow—such as the heart rate.
However to date, such techniques have not been used for the blood pressure determinations. What is needed, therefore, is a blood pressure measurement apparatus and process that is continuous, non-invasive and accurate.